The present invention relates to electrically operated servo-actuators for providing mechanical movement of a mechanism in response to an electrical control signal. Servo-actuators of this type are employed in various control applications, such as, for example, throttle actuators employed for motor vehicle operation
It has been proposed to provide all-electrical operation of a vehicle throttle by utilizing an electrical throttle actuator mechanism controlled electronically in response to electrical input signals generated by various operating parameters and a signal generated by the driver varying the position of the vehicle accelerator pedal. Such all-electrical control of the vehicle throttle thus eliminates the commonplace cable or linkage connection between the vehicle accelerator pedal and the vehicle engine throttle. This type of vehicle throttle control offers a high degree of sophistication of engine operational control because the electronic computer or microprocessor can provide changes in the electrical control signal, responsive to selected electrical sensory inputs, much faster than human reaction time.
However, all-electrical control of a vehicle throttle has the inherent disadvantages that failure of the electronic controller requires expensive and complicated redundancy or back-up to prevent total loss or uncontrollable vehicle motive power and particularly in the event that the microprocessor in the controller fails completely or operates in an unacceptable manner.
It has been desired to provide a system for incorporating electrical control of a vehicle throttle for certain modes of operation, as for example, traction control and cruise control where it is desirable to take advantage of the speed of response of a microprocessor-based controller. It has also been desired to maintain a mechanical cable or linkage connection between the accelerator pedal and the vehicle throttle to provide the driver with redundant control in the event of failure of the electronic controller. A system of this latter type is sometimes referred to as a throttle cable intervention system. However, where it is desired to incorporate plural mode functions in a single electrically operated electronically controlled actuator it has proven prohibitively costly and complex to employ a single actuator device which could operate in both modes and yet be compatible with a particular mechanical load. It has thus been desired to provide a way or means of combining in a single motor-driven servoactuator a dual mode function of operation for the motor driven mechanism of the servo; and, in particular, to provide such a servo for application in combining cruise control function and traction control functions in a motor vehicle throttle actuator application while retaining the mechanical interconnection of the accelerator pedal and the engine throttle.